HAHA
1. Nvidia recommends that, on boards with three slots available, you use the first and third, leaving room between.
2. In short, GTX 480s back to back is a bad idea.
3. A beefy power supply is a given, though Nvidia hasn’t yet recommended the best wattage for a dual-GPU setup. "
1. so what if your board only has 2 slots?
2. putting 2 gtx480's back to back turns your computer into an oven.
3. nVidia recommends 3 phase to the house at a minimum.
What happened nVidia?? not only did you drop the ball, you kicked it away.